The present invention relates to a method of preparing a nonwoven web having delayed wettability. More particularly, the present invention relates to a method of increasing the delay period of a nonwoven web which is not wettable by water upon its formation but which becomes wettable thereafter without any post-formation treatment.
Cross-referenced application Ser. No. 07/485,922 describes a method of preparing a nonwoven web which is not wettable by water immediately after its formation but which becomes wettable within about 24 hours thereafter without any post-formation treatment. The method comprises melting a mixture of at least one thermoplastic polyolefin and at least one additive having the general formula, ##STR2## and extruding the resulting melt through a die at a shear rate of from about 50 to about 30,000 sec.sup.-1 and a throughput of no more than about 5.4 kg/cm/hour, in which: (A) R.sub.1 -R.sub.7 are independently selected monovalent C.sub.1 -C.sub.3 alkyl groups;
(B) R.sub.8 is hydrogen or a monovalent C.sub.1 -C.sub.3 alkyl group; PA1 (C) m represents an integer of from 0 to about 5 PA1 (D) n represents an integer of from 3 to about 8; PA1 (E) said additive has a molecular weight of from about 350 to about 700; PA1 (F) said additive has a polydispersity of from about 1.0 to about 1.3; and PA1 (G) said additive is present in an amount of from about 0.5 to about 1.75 percent by weight, based on the amount of thermoplastic polymer, which amount, if homogeneously distributed throughout the polyolefin, is not sufficient to render the polyolefin wettable by water. PA1 (A) R.sub.1 -R.sub.7 are independently selected monovalent C.sub.1 -C.sub.3 alkyl groups; PA1 (B) R.sub.8 is hydrogen or a monovalent C.sub.1 -C.sub.3 alkyl group; PA1 (C) m represents an integer of from 0 to about 5 PA1 (D) n represents an integer of from 3 to about 8; PA1 (E) said additive has a molecular weight of from about 350 to about 700; PA1 (F) said additive has a polydispersity of from about 1.0 to about 1.3; and PA1 (G) said additive is present in an amount of from about 0.5 to about 1.75 percent by weight, based on the amount of thermoplastic polyolefin, which amount, if homogeneously distributed throughout the polyolefin, is not sufficient to render the polyolefin wettable by water;
It was discovered that the inclusion of a phthalocyanine dye in the composition to be melt-processed resulted in a nonwoven web having a significantly increased delay period relative to a composition in which the phthalocyanine dye was absent. Thus, it is evident that materials exist which have the unusual and unexpected capacity to increase the delay period in nonwoven webs prepared in accordance with the method described in application Ser. No. 07/485,922.